U.S. patent number 7,540,470 [Application Number 11/382,298] was granted by the patent office on 2009-06-02 for powdered metal inlay.
Invention is credited to George H. Blume.
United States Patent |
7,540,470 |
Blume |
June 2, 2009 |
Powdered metal inlay
Abstract
Hot-isostatic-pressure (HIP) is used to make substantially
nonporous cemented carbide inlays on metal substrates. A radiused
shell preform typically comprising at least one metal carbide and
at least one nonvolatile cement is shaped as a rigid frusto-conical
shell having a substantially uniform thickness and a predetermined
radius on every edge. HIP pressure is applied via a conforming
adjustable sliding element to compress the preform against a
conforming substrate. Surfaces of the conforming adjustable sliding
element and conforming substrate, and/or the radiused shell
preform, may in certain embodiments be coated substantially
uniformly with at least one nonvolatile cement. Space around a
radiused shell preform is evacuated without the need to totally
enclose the radiused shell preform and its substrate in a can.
Certain embodiments provide for leak testing of welded seals prior
to application of HIP, and other embodiments make the use of welded
seals unnecessary.
Inventors: |
Blume; George H. (Austin,
TX) |
Family
ID: |
40672351 |
Appl.
No.: |
11/382,298 |
Filed: |
May 9, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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11032888 |
Jan 11, 2005 |
7070166 |
|
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Current U.S.
Class: |
251/333;
29/890.129; 29/890.122; 29/888.3; 251/359; 137/902; 137/15.18 |
Current CPC
Class: |
F16K
31/041 (20130101); F04B 53/1087 (20130101); F16K
1/465 (20130101); F04B 53/102 (20130101); F16K
15/06 (20130101); B22F 3/15 (20130101); F04B
53/1082 (20130101); Y10T 137/0491 (20150401); Y10S
137/902 (20130101); Y10T 29/49421 (20150115); B22F
2003/153 (20130101); Y10T 29/49409 (20150115); B22F
5/008 (20130101); Y10T 29/49297 (20150115) |
Current International
Class: |
F16K
51/00 (20060101) |
Field of
Search: |
;251/359,365,333,334
;29/890.122,888.3,890.129 ;137/15.18,902 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bastianelli; John
Attorney, Agent or Firm: Gilstad; Dennis W.
Claims
What is claimed is:
1. A valve seat form comprising: a circular wall around a
cylindrical void, said circular wall being substantially
symmetrical about a longitudinal axis and having a first end spaced
apart from a second end, as well as an inner surface spaced apart
from an outer surface; a circular depression in said circular wall
first end between said circular wall inner and outer surfaces, said
circular depression comprising cylindrical inner and outer
depression walls coaxial with said circular wall, said inner and
outer depression walls being spaced apart from each other and
extending from said circular wall first end toward said circular
wall second end to a depression bottom surface, said depression
bottom surface extending between said inner depression wall and
said outer depression wall and conforming to a radiused shell
preform shaped as a rigid frusto-conical steel symmetrical about
said longitudinal axis and having a substantially uniform thickness
and a predetermined radius on every edge, each said radius being
about 10% to about 50% of said uniform thickness; and a transverse
web extending from said circular wall inner surface completely
across said cylindrical void adjacent to said circular wall first
end, peripheral portions of said transverse web being integral with
said circular wall inner surface.
2. The valve seat form a claim 1 wherein said circular wall
comprises H13 tool steel.
3. The valve seat form of claim 1 wherein said frusto-conical shell
is sloped at an angle between about 20 degrees and about 60 degrees
with respect to said longitudinal axis.
4. The valve seat form of claim 2 additionally comprising a
peripheral circular rim on said circular wall first end, said
circular rim being usable for centering and peripherally
hermetically sealing a deformable circular lid extending over said
circular depression and said transverse web.
5. The valve seat form of claim 1, wherein said transverse web
comprises a shallow concavity substantially symmetrical about said
longitudinal axis and extending toward said circular wall second
end.
6. A valve seat HIPPING assembly comprising the valve seat form of
claim 4 and additionally comprising: a radiused steel preform to
which said depression bottom surface conforms, said radiused shell
preform being located within said circular depression; a circular
ring having an obverse face and a reverse face and being sealingly
movable longitudinally within said circular depression to compress
said radiused shell preform between said obverse face and said
depression bottom surface, said obverse face conforming to said
radiused shell preform; and a deformable circular lid centerable
within said peripheral circular rim on said circular wall first
end, said deformable circular lid extending over said circular
depression and said transverse web, and said deformable circular
lid being peripherally hermetically sealable to said peripheral
circular rim.
7. The valve seat HIPPING assembly of claim 6 wherein said
frusto-conical shell is sloped at an angle between about 20 degree
and about 60 degrees with respect to said longitudinal axis.
8. The valve seat HIPPING assembly of claim 6 wherein and said
radiused shell preform comprises tungsten carbide and cobalt.
9. The valve seat HIPPING assembly of claim 6 wherein said
transverse web comprises a shallow concavity substantially
symmetrical about said longitudinal axis and extending toward said
circular wall second end.
10. The valve seat HIPPING assembly of claim 6 wherein said
deformable circular lid and said circular ring are formed as a
single circular lid-ring structure, said circular lid-ring being
peripherally hermetically sealable to said peripheral circular rim,
and said circular lid-ring being deformable to allow longitudinal
movement toward said depression bottom surface.
11. A valve seat HIPPING assembly comprising the valve seat form of
claim 2 and additionally comprising: a radiused shell preform to
which said depression bottom surface conforms, said radiused shell
preform being located within said circular depression; a circular
ring having an obverse face and a reverse face and being sealingly
movable longitudinally within said circular depression to compress
said preform between said obverse face and said depression bottom
surface, said obverse face conforming closely to said preform and
said circular ring being hermetically sealable to said circular
wall first end.
12. The valve seat HIPPING assembly of claim 11 wherein said
frusto-conical shell is sloped at an angle between about 20 degrees
and about 60 degrees with respect to said longitudinal axis.
13. A method of making a HIPPED valve seat inlay using the valve
seat HIPPING assembly of claim 9, the method comprising: providing
the valve seat HIPPING assembly of claim 9; inserting said valve
seat HIPPING assembly in a vacuum chamber; evacuating said vacuum
chamber to about 0.1 torr; peripherally hermetically sealing said
deformable circular lid to said peripheral circular rim to form an
evacuated valve seat assembly; increasing ambient pressure on said
evacuated valve seat assembly to atmospheric pressure; testing said
evacuated valve seat assembly for a shallow concavity in said
deformable circular lid, said shallow concavity being substantially
symmetrical about said longitudinal axis and extending toward said
circular wall second end; heating said evacuated valve seat
assembly sufficiently to make said radiused shell preform plastic,
thus forming a heated evacuated valve seat assembly; applying an
ambient pressure of at least about 15,000 pounds per square inch to
said heated evacuated valve seat assembly to form a consolidated
valve seat inlay assembly; gas quenching said consolidated valve
seat inlay assembly to form a quenched valve seat inlay assembly;
tempering said quenched valve seat inlay assembly to form a
tempered valve seat inlay assembly; and finish machining said
tempered valve seat inlay assembly to make a HIPPED valve seat
inlay.
14. A valve comprising a finish-machined valve seat inlay made
according to the method of claim 13.
15. A method of making a HIPPED valve seat inlay using the valve
seat HIPPING assembly of claim 10, the method comprising: providing
the valve seat HIPPING assembly of claim 10; inserting said valve
seat HIPPING assembly in a vacuum chamber; evacuating said vacuum
chamber to about 0.1 torr; peripherally hermetically sealing said
deformable circular lid-ring to said peripheral circular rim to
form an evacuated valve seat assembly; increasing ambient pressure
on said evacuated valve seat assembly to atmospheric pressure;
testing said evacuated valve seat assembly for a shallow concavity
in said deformable circular lid-ring, said shallow concavity being
substantially symmetrical about said longitudinal axis and
extending toward said circular wall second end; heating said
evacuated valve seat assembly sufficiently to make said radiused
shell preform plastic, thus forming a heated evacuated valve seat
assembly; applying an ambient pressure of at least about 15,000
pounds per square inch to said heated evacuated valve seat assembly
to form a consolidated valve seat inlay assembly; gas quenching
said consolidated valve seat inlay assembly to form a quenched
valve seat inlay assembly; tempering said quenched valve seat inlay
assembly to form a tempered valve seat inlay assembly; and finish
machining said tempered valve seat inlay assembly to make a HIPPED
valve seat inlay.
16. A valve comprising a finish-machined valve seat inlay made
according to the method of claim 15.
17. A method of making a HIPPED valve seat inlay using the valve
seat HIPPING assembly of claim 11, the method comprising: providing
the valve seat HIPPING assembly of claim 11; inserting said valve
seat HIPPING assembly in a vacuum chamber; evacuating said vacuum
chamber to about 0.1 torr; hermetically sealing said circular ring
to said circular wall first end to form an evacuated valve seat
assembly; heating said evacuated valve seat assembly sufficiently
to make said radiused shell preform plastic, thus forming a heated
evacuated valve seat assembly; applying an ambient pressure of at
least about 15,000 pounds per square inch to said heated evacuated
valve seat assembly to form a consolidated valve seat inlay
assembly; gas quenching said consolidated valve seat inlay assembly
to form a quenched valve seat inlay assembly; tempering said
quenched valve seat inlay assembly to form a tempered valve seat
inlay assembly; and finish machining said tempered valve seat inlay
assembly to make a HIPPED valve seat inlay.
18. A valve comprising a finish-machined valve seat inlay made
according to the method of claim 17.
19. A valve seat form comprising a circular wall around a
cylindrical void, said circular wall being substantially
symmetrical about a longitudinal axis and having a first end spaced
apart from a second end, as well as an inner surface spaced apart
from an outer surface; and a circular depression in said circular
wall first end between said circular wall inner and outer surfaces,
said circular depression comprising cylindrical inner and outer
depression walls coaxial with said circular wall, said inner and
outer depression walls being spaced apart from each other and
extending from said circular wall first end toward said circular
wall second end to a depression bottom surface, said depression
bottom surface extending between said inner depression wall and
said outer depression wall and conforming to a radiused shell
preform shaped as a rigid frusto-conical steel symmetrical about a
longitudinal axis and having a substantially uniform thickness and
a predetermined radius on every edge, each said radius being about
10% to about 50% of said uniform thickness.
20. A valve seat HIPPING assembly comprising the valve seat form of
claim 19 and additionally comprising: a valve seat plug for
insertion slidingly and sealingly within said circular wall
cylindrical void from said circular wall second end, said valve
seat plug comprising a flange for contacting said circular wall
second end to limit insertion of said valve seat plug into said
circular wall cylindrical void; and at least one circumferential
seal for sealing said valve seat plug against said circular wall
inner surface during sliding insertion of said valve seat plug
within said circular wall cylindrical void; a radiused shell
preform located within said circular depression and shaped as a
rigid frusto-conical steel symmetrical about a longitudinal axis
and having a substantially uniform thickness and a predetermined
radius on every edge, each said radius being about 10% to about 50%
of said uniform thickness; a circular ring having an obverse face
and a reverse face and being sealingly movable longitudinally
within said circular depression to compress said radiused shell
preform between said obverse face and said depression bottom
surface, said obverse face conforming closely to said radiused
shell preform; and a circular top cap fitting slidingly and
sealingly over said circular wall first end and said circular ring,
said circular top cap being movable longitudinally to contact said
circular ring reverse face for moving said circular ring
longitudinally within said circular depression toward said
depression bottom surface, said circular top cap comprising at
least one evacuation/pressurization port usable for evacuating
space enclosed by said circular wall, said circular top cap, and
said valve seat plug; and at least one internal circumferential
seal for sealing said circular top cap against said circular wall
outer surface as said circular top cap is fitted slidingly over
said circular wall first end.
21. A valve seat HIPPING assembly comprising the valve seat form of
claim 19 and additionally comprising: a radiused shell preform
located within said circular depression and shaped as a rigid
frusto-conical shell symmetrical about a longitudinal axis and
having a substantially uniform thickness and a predetermined radius
on every edge, each said radius being about 10% to about 50% of
said uniform thickness; a circular ring having an obverse face and
a reverse face and being sealingly movable longitudinally within
said circular depression to compress said radiused shell preform
between said obverse face and said depression bottom surface, said
obverse face conforming closely to said radiused shell preform; and
a circular top cap fitting slidingly and sealingly over said
circular wall first end and said circular ring, said circular top
cap being movable longitudinally to contact said circular ring
reverse face for moving said circular ring longitudinally within
said circular depression toward said depression bottom surface,
said circular top cap comprising at least one
evacuation/pressurization port usable for evacuating space enclosed
by said circular wall, said circular top cap, and said circular
ring; at least one internal circumferential seal for sealing said
circular top cap against said circular wall outer surface as said
circular top cap is fitted slidingly over said circular wall first
end; and a shallow counterbore centered within said circular top
cap, said shallow counterbore being dimensioned to fit slidingly
and sealingly over said circular ring, and said shallow counterbore
having at least one circular seal for sealing against said circular
ring as said circular ring is fitted slidingly within said shallow
counterbore.
22. A valve seat HIPPING assembly comprising the valve seat
substrate of claim 1 and additionally comprising: a radiused shell
preform located within said circular depression and shaped as a
rigid frusto-conical steel symmetrical about a longitudinal axis
and having a substantially uniform thickness and a predetermined
radius on every edge, each said radius being about 10% to about 50%
of said uniform thickness; a circular ring having an obverse face
and a reverse face and being sealingly movable longitudinally
within said circular depression to compress said radiused shell
preform between said obverse face and said depression bottom
surface, said obverse face conforming closely to said radiused
shell preform; and a circular top cap fitting slidingly and
sealingly over said circular wall first end and said circular ring,
said circular top cap being movable longitudinally to contact said
circular ring reverse face for moving said circular ring
longitudinally within said circular depression toward said
depression bottom surface, said top cap comprising at least one
evacuation/pressurization port usable for evacuating space enclosed
by said circular wall, said circular top cap, and said transverse
web; and at least one internal circumferential seal for sealing
said circular top cap against said circular wall outer surface as
said circular top cap is fitted slidingly over said circular wall
first end.
23. The valve seat assembly of claim 22 additionally comprising
ring retention means for temporarily retaining said circular ring
within said circular top cap; and ring centering means for
centering said circular ring within said circular top cap.
24. A valve seat form comprising a circular wall around a
cylindrical void, said circular wall being substantially
symmetrical about a longitudinal axis and having a first end spaced
apart from a second end, as well as an inner surface spaced apart
from an outer surface; a circular depression in said circular wall
first end between said circular wall inner and outer surfaces, said
circular depression comprising cylindrical inner and outer
depression walls coaxial with said circular wall, said inner and
outer depression walls being spaced apart from each other and
extending from said circular wall first end toward said circular
wall second end to a depression bottom surface, said depression
bottom surface extending between said inner depression wall and
said outer depression wall and conforming to a radiused shell
preform shaped as a rigid frusto-conical shell symmetrical about
said longitudinal axis and having a substantially uniform thickness
and a predetermined radius on every edge, each said radius being
about 10% to about 50% of said uniform thickness; and a transverse
web extending from said circular wall inner surface completely
across said cylindrical void adjacent to said circular wall first
end, peripheral portions of said transverse web being integral with
said circular wall inner surface; wherein said conforming
depression bottom surfacer is coated substantially uniformly with
at least one nonvolatile cement.
25. The valve seat form of claim 24 wherein said at least one
nonvolatile cement comprises cobalt.
26. A valve seat HIPPING assembly comprising the valve seat form of
claim 24 and additionally comprising: a radiused shell preform to
which said depression bottom surface conforms, said radiused shell
preform being located within said circular depression; a circular
ring having an obverse face and a reverse face and being sealingly
movable longitudinally within said circular depression to compress
said radiused shell preform between said obverse face and said
depression bottom surface, said obverse face being coated
substantially uniformly with at least one nonvolatile cement and
conforming to said radiused shell preform; and a deformable
circular lid centered within said peripheral circular rim on said
circular wall first end, said deformable circular lid extending
over said circular depression and said transverse web, and said
deformable circular lid being peripherally hermetically sealable to
said peripheral circular rim.
27. The valve seat HIPPING assembly of claim 26 wherein said at
least one nonvolatile cement comprises cobalt.
Description
FIELD OF THE INVENTION
The invention relates generally to inlays comprising one or more
metal carbides on metal substrates such as valve components.
BACKGROUND
Valve terminology varies according to the industry (e.g., pipeline
or oil field service) in which the valve is used. In some
applications, the term "valve" means just the valve body, which
reversibly seals against the valve seat. In other applications, the
term "valve" includes components in addition to the valve body,
such as the valve seat and the housing that contains the valve body
and valve seat. A valve assembly of the invention comprises a valve
body and a corresponding valve seat, the valve body typically
incorporating an elastomeric seal within a peripheral seal
retention groove.
Valve assemblies of the invention can be mounted in the fluid end
of a high-pressure pump incorporating positive displacement pistons
or plungers in multiple cylinders. Such valve assemblies typically
experience high pressures and repetitive impact loading of the
valve body and valve seat. These severe operating conditions have
in the past often resulted in leakage and/or premature valve
failure due to metal wear and fatigue. In overcoming such failure
modes, special attention is focused in the invention on valve
sealing surfaces where the valve body contacts the valve seat
intermittently for reversibly blocking fluid flow through a valve
assembly.
Valve assembly sealing surfaces are subject to exceptionally harsh
conditions in exploring and drilling for oil and gas, as well as in
their production. For example, producers often must resort to
"enhanced recovery" method to insure that an oil well is producing
at a rate that is profitable. And one of the most common methods of
enhancing recovery from an oil well is known as fracturing. During
fracturing, cracks are created in the rock of an oil bearing
formation by application of high hydraulic pressure. Immediately
following fracturing, a slurry comprising sand and/or other
particulate material is pumped into the cracks under high pressure
so they will remain propped open after hydraulic pressure is
released from the well. With the cracks thus held open, the flow of
oil through the rock formation toward the well is usually
increased.
The industry term for particulate material in the slurry used to
prop open the cracks created by fracturing is the propend. And in
cases of very high pressures within a rock formation, the propend
may comprise extremely small aluminum oxide spheres instead of
sand. Aluminum oxide spheres may be preferred because their
spherical shape gives them higher compressive strength than angular
sand grains. Such high compressive strength is needed to withstand
pressures tending to close cracks that were opened by fracturing.
Unfortunately, both sand and aluminum oxide slurries are very
abrasive, typically causing rapid wear of many component parts in
the positive displacement plunger pumps through which they flow.
Accelerated wear is particularly noticeable in plunger seals and in
the suction (i.e., intake) and discharge valve assemblies of these
pumps.
A valve assembly 10 (comprising a valve body 20 and valve seat 40)
that is representative of an example full open design valve and
seat for a fracturing plunger pump is schematically illustrated in
FIG. 1. FIG. 2 shows how sand and/or aluminum oxide spheres may
become trapped between sealing surface 21 of valve body 20 and
sealing surface 41 of valve seat 40 as the suction valve assembly
10 closes during the pump's pressure stroke.
The valve assembly 10 of FIG. 1 is shown in the open position. FIG.
2 shows how accelerated wear begins shortly after the valve starts
to close due to back pressure. For valve assembly 10, back pressure
tends to close the valve when downstream pressure exceeds upstream
pressure. For example, when valve assembly 10 is used as a suction
valve, back pressure is present on the valve during the pump
plunger's pressure stork (i.e., when internal pump pressure becomes
higher than the pressure of the intake slurry stream. During each
pressure stroke, when the intake slurry stream is thus blocked by a
closed suction valve, internal pump pressure rises and slurry is
discharged from the pump through a discharge valve. For a discharge
valve, back pressure tending to close the valve arises whenever
downstream pressure in the slurry stream (which remains relatively
high) becomes greater than internal pump pressure (which is briefly
reduced each time the pump plunger is withdrawn as more slurry is
sucked into the pump through the open suction valve).
When back pressure begins to act on a valve, slurry particles
become trapped in the narrow space that still separates the sealing
metal surfaces of the valve body and seat. This trapping occurs
because the valve is not fully closed, but the valve body's
elastomeric seal has already formed an initial seal against the
valve seat. The narrow space shown in FIG. 2 between metallic
sealing surfaces 21 and 41 of the valve body and valve seat
respectively is typically about 0.040 to about 0.080 inches wide;
this width (being measured perpendicular to the sealing surfaces of
the valve body and seat) is called the standoff distance. The size
of the standoff distance is determined by the portion of the valve
body's elastomeric seal that protrudes beyond the adjacent valve
body sealing surfaces to initially contact, and form a seal
against, the valve seat. As schematically illustrated in FIG. 2,
establishment of this initial seal by an elastomeric member creates
a circular recess or pocket that tends to trap particulate matter
in the slurry flowing through the valve.
Formation of an initial seal as a valve is closing under back
pressure immediately stops slurry flow through the valve. Swiftly
rising back pressure tends to drive slurry backwards through the
now-sealed valve, but since back-flow is blocked by the initial
valve sealing, pressure builds rapidly on the entire valve body.
This pressure acts on the area of the valve body circumscribed by
its elastomeric seal to create a large force component tending to
completely close the valve. For example, a 5-inch valve exposed to
a back pressure of 15,000 pounds per square inch will experience a
valve closure force that may exceed 200,000 pounds.
The large valve closure force almost instantaneously drives the
affected valve assembly, whether suction or discharge, to the fully
closed position where the metal sealing surface of the valve body
contacts the corresponding metal sealing surface of the valve seat.
As the valve body moves quickly through the standoff distance
toward closure with the valve seat, the elastomeric seal insert is
compressed, thus forming an even stronger seal around any slurry
particles that may have been trapped between the seal insert and
the valve seat.
Simultaneously, the large valve closure force acting through the
standoff distance generates tremendous impact energy that is
released against the slurry particles trapped between the metallic
sealing surfaces of the valve body and the valve seat. As shown in
FIG. 3, the slurry particles that are trapped between approaching
valve sealing surfaces 21 and 41 are crushed.
In addition to the crushing action described above, slurry
particles are also dragged between the valve sealing surfaces in a
grinding motion. This grinding action occurs because valve bodies
and seats are built with complementary tapers on the sealing
surfaces to give the valve assembly a self-alignment feature as the
valve body closes against the seat. As the large valve closing
force pushes the valve body into closer contact with the seat, the
valve body tends to slide down the sealing surface taper by a very
small amount. Any crushed slurry particles previously trapped
between the sealing surfaces are then ground against these
surfaces, resulting in extreme abrasive action.
To limit sealing surface erosion due to this abrasion, valve bodies
and seats have in the past been heat-treated to harden and
strengthen them. Typical heat treatment methods have included
carburizing, as well as hardening by induction heating and flame
hardening. All of these hardening processes depend on quenching
(i.e., rapid cooling) of the valve components after they have been
uniformly heated, preferably slightly above a critical temperature
(called the upper transformation temperature).
When a steel object is uniformly heated to a temperature slightly
above its upper transformation temperature, all of the steel in the
object assumes a face-centered cubic crystal lattice structure
known as austenite. When the object is quenched below this
temperature, other crystal lattice structures are possible. If
quenched uniformly, the other crystal lattice structures tend to
appear uniformly throughout the object. But if certain portions of
the object are cooled at rates different from those applicable to
other portions of the object, then the crystal lattice structure of
the cooled object may be non-uniform.
Further, if steel is heated too far above its upper transformation
temperature before quenching, its grain structure may be
unnecessarily coarsened, meaning that the steel will then be less
tough and more brittle after quenching than it would have been if
its maximum temperature had been closer to its upper transformation
temperature. It is therefore important that heat treatments for a
particular steel be applied uniformly when uniform results are
desired, and it is further important that maximum temperatures not
be so high as to adversely affect the steel's grain structure.
Quenching is performed primarily to influence the formation of a
desirable crystal lattice and/or grain structure in a cooled metal,
a grain being a portion of the metal having external boundaries and
a regular internal lattice. Quenching may be accomplished, for
example, simply by immersion of a heated metal object in water or
oil. Certain tool steels may even be quenched by gas (e.g., air or
inert gas), but the carbon steels traditionally used for valve
seats can not be gas-quenched if they are to develop the hardness,
strength and toughness necessary for use in high-pressure
valves.
Heat treating of metals has been extensively studied, and many
desirable properties may be obtained in metals through elaborate
quench and temper protocols that have been experimentally
developed. But preferred heat treatments are highly specific to
particular alloys, so there may be no single optimal heat treatment
for a component such as a valve seat comprising, for example, a
high-alloy sealing surface inlay on a carbon steel substrate.
Indeed, even the most careful use of heat treatment to favor
development of hard sealing surfaces on strong, tough substrates
has not proven effective for extending the service life of valves
traditionally used for high-pressure abrasive slurries. Thus,
engineers have long sought better methods of hardening valve
sealing surfaces at acceptable cost.
For example, incorporation of metallic carbides in sealing surfaces
has been investigated because some metallic carbides are extremely
hard and wear-resistant. But such carbides do not bond well with
the low-carbon steels commonly used in high pressure valve seats.
Hence, when metallic carbide inlays are applied to such valve seat
substrates, they must actually be held in place by some type of
cement which itself forms an adequate bond with the valve seat
substrate steel.
To facilitate mixing metallic carbides with cement(s), the carbides
are made commercially available in powder form. Such powders (e.g.,
carbides of vanadium, molybdenum, tungsten or chromium) are formed
by casting the pure carbides and then crushing them into the
desired particle size. A cement (comprising, e.g., cobalt,
chromium, and/or nickel) is then added to the crushed carbide
powders, but there is little or no opportunity for the cement to
alloy with the carbides.
Metallic carbide particles thus bound as an inlay on a steel
substrate are called cemented carbides, and they comprise a matrix
consisting of a dispersion of very hard carbide particles in the
(relatively softer) cement. The resulting cemented carbide inlays
are thus not homogeneous, so they do not possess the uniform
hardness that would ideally be desired for good abrasion resistance
and toughness in valve sealing surfaces. One problem associated
with this inhomogeneity becomes evident because the crushing and
grinding of slurry particles between valve sealing surfaces during
valve closure produces a variety of slurry particle sizes, some so
fine that they are smaller than the spacing between the carbide
particles in the cemented carbide inlay. These fine slurry
particles are very abrasive, and if they can fit between the
carbide particles they can rapidly wear away the relatively soft
cement holding the carbide particles in place. Thus loosened (but
not actually worn down), the carbide particles can simply be
carried away by the slurry stream, leaving the remainder of the
inlay cement exposed to further damage by the abrasive slurry.
Problems associated with inhomogeneity of cemented carbide inlays
may be reduced by choosing relatively high carbide content (e.g.,
about 85% to about 95%) and sub-micron carbide particle size. Such
results have been confirmed by testing according to ASTM B 611
(Test Method for Abrasive Wear Resistance of Cemented
Carbides).
Notwithstanding the above problems, cemented carbides, particularly
those applied by gas-fueled or electrically-heated welding
equipment, have been widely used to reduce abrasion damage in
various industrial applications. But weld-applied carbide inlays
have not been found acceptable in high pressure valves. This is due
in part to a need for relatively high cement content in
weld-applied inlays, leading to relatively high porosity inlays
having low abrasion resistance and a predisposition to multiple
internal stress risers. Low abrasion resistance results from wide
spacing of wear-resistant carbide particles, separated by
relatively softer cement. And the internal stress risers exacerbate
cracking of brittle cemented carbide inlays under the repetitive
high-impact loading common in high pressure valves. The result has
typically been an increased likelihood of premature (often
catastrophic) valve failures. Thus, a long-felt need remains for
better technology that can be economically applied to harden valve
sealing surfaces while avoiding an excessive likelihood of
cracking.
While such cracks are tolerated in certain applications where the
cracks do not significantly affect the performance of the part, the
same can not be said of high pressure valve assemblies. On the
contrary, cyclic fatigue associated with the repeated large impact
loads experienced by these values magnifies the deleterious effects
of cracks and residual stresses that may result from differentials
in coefficients of thermal expansion. Premature catastrophic
failures of valve bodies and/or seats are a frequent result.
To address the problem of cracking in high-pressure valve seats,
relatively high-carbide tool steel cladding has been applied on low
carbon steel substrates. The tool steel cladding is commercially
available as a powder in which all the elements have been mixed,
melted and then gas atomized into spheres. High grades of these
tool steel cladding powders are called P/M (for particle
metallurgy) grades, and they generally cost at least 10 times per
unit weight more than lower grade tool steels. Notwithstanding the
high grade and high cost of the tool steel cladding however, these
experimental valve seats have not been successful because the
reheat treatment required to reduce the cladding's brittleness does
not simultaneously cause development of the required strength and
toughness in the low-carbon steel substrate. Further, tool steel
powders are limited to carbide concentrations of about 25%, whereas
cemented carbides can have carbide concentrations of about 75% to
95%.
The above-noted difficulty of reducing the brittleness of a
relatively high carbide P/M inlay while simultaneously developing
strength and toughness in a low-carbon steel substrate may be
addressed by substituting low grade tool steel (e.g., H13) for the
low-carbon steel of the substrate. Residual internal stress is
thereby reduced because a cladding matrix of high alloy P/M powder
has a coefficient of thermal expansion which closely matches that
of a low grade tool steel substrate. Such close matching of thermal
expansion coefficients is not seen with inlays of either cemented
carbide or tool steel on a low-carbon steel substrate. Further,
during the melting and atomization of P/M alloys, the elements
combine to form very fine carbides. Some of the carbon and other
elements in the P/M powder alloy with the iron to form very high
alloy steel, and some of the carbides are then able to alloy with
the steel. The combination of the high alloy steel and the very
fine alloyed carbides give cladding comprising such P/M tool steel
the effect of having nearly uniform hardness and homogeneity
throughout.
A typical process of forming P/M grade tool steels comprises
induction melting of a pre-alloyed tool steel composition, followed
by gas atomization to produce a rapidly solidified spherical
powder. This powder may then be applied to a base steel substrate
by either weld overlay or, preferably, by hot isostatic pressure
(HIP). Of course, the substrate could be eliminated if P/M powder
were used to form an entire structure such as a valve seat by use
of HIP (i.e., by HIPPING), but the cost of a valve seat comprising
100% of P/M grade tool steels would be prohibitive. And in spite of
its high cost, such a valve seat would lack the toughness and
strength otherwise obtainable if mild steel or a lower grade tool
steel were used as a substrate.
HIP is a preferred method of applying a P/M grade inlay to a
substrate because welding degrades some of the potential desirable
properties of the inlay. Even when welded ideally, a P/M inlay will
lose its fine microstructure in the weld fuse zone, where it melts
during welding. Thus, P/M grades, when welded, do not achieve
optimal toughness. Further, the melting that occurs during welding
will decarburize some of the carbides, decreasing wear resistance.
For these reasons, using welding to apply the high alloy P/M grades
on heavy impact areas such as a valve seat will always present some
risk of cracking in service. Rather, to make best use of high alloy
P/M grades, they must be applied by HIP.
The HIP process avoids problems associated with welding because HIP
is carried out at a temperature that is slightly lower than the
melting temperature of the material being HIPPED. In fact, the
ideal HIP temperature is the temperature at which the HIPPED
material is only slightly plastic.
In current industry practice, HIP-applied inlays as described above
require that the P/M powder be subjected to heat and pressure in a
sealed enclosure (e.g., a metal can) which is evacuated to less
than 0.1 torr (i.e., less than 0.1 mmHg). Empirical data show that
this high vacuum is needed to reduce the inlay's porosity to
achieve an inlay density of at least 99.7%. High density of the
inlay is necessary to prevent formation of porous defects in the
finished valve seat. Such porous defects, if present under cyclic
fatigue impact loading, act as stress risers which lead to cracks,
crack propagation, and catastrophic failure. Establishment of a
high vacuum within the sealed HIP enclosure reduces these problems
and also avoids undesirable oxidation of both the tool steel
substrate and the P/M powder inlay during subsequent heat
treatment.
In some pre-HIP applications, P/M powder may be performed into a
shape corresponding to the final inlay position on the substrate.
This performing is generally done independent of the substrate
itself. Powder preforms are commonly made using a Cold Isostatic
Pressure (CIP) process in which the powder is forged into a
physical shape that, while porous (typically about 50% voids), is
held intact at the inlay position by mechanical bonds among the
powder particles and/or by a binder such as wax or a polymer.
Typically, CIP is applied by placing the P/M powder in some type of
deformable mold (e.g., rubber) having the desired shape and then
pressurizing the mold. The pressurized deformable mold then
collapses on the powder, compressing it under very high pressure
(typically at least 30,000 psi.). After this compression and prior
to HIPPING, any relativity volatile binder such as wax or polymer
must be removed or driven off (e.g., by the heat of
presintering).
Higher grade P/M powders are generally compressed at relatively
high CIP pressures to achieve the necessary structural integrity
for a powder preform to prepare it for subsequent application of
HIP. This is because the greater hardness of these P/M powders
makes the powder particles relatively resistant to the deformation
required to achieve sufficiently strong mechanical bonds among the
particles. These mechanical bonds may be augmented by use of a
binder (e.g., a wax or polymer), although such binders must then be
removed prior to HIPPING. Even greater preform structural
integrity, as well as increased density and the elimination of
volatile binders such as wax or polymer, may be achieved by heating
a compressed powder preform to presinter or sinter it. A sintered
preform will generally be more likely to retain its shape during
handling than a presintered preform, but sintering also encourages
metallic grain growth that is associated with preform
brittleness.
A metal can used for application of HIP may, if it provides
complete sealing around a preform and substrate, facilitate
evacuation of the space adjacent to the inlay as described above.
For example, the can used in current industry practice for the
powder preform has welded seams and completely surrounds both inlay
and substrate. A cross-section of such a typical welded can
assembly with its enclosed valve seat substrate and inlay is shown
in FIG. 4.
Note that a welded can assembly analogous to that of FIG. 4 usually
has an evacuation tube. When present, such a tube allows evacuation
of the can assembly after it is welded together (with the
evacuation tube then being crimped/welded shut to maintain the
vacuum within the can assembly). If a can assembly does not have an
evacuation tube, this means that the can assembly itself must be
welded together in a high-vacuum environment using a technique,
such as electron beam welding, which is suitable for welding in a
vacuum.
Since the can assembly in FIG. 4 does have an evacuation tube, it
may be welded together using conventional techniques. The welded
can assembly is tested for leaks with helium, after which the
helium and any residual air are then evacuated via the evacuation
tube. After evacuation, the evacuation tube is first crimped shut
and then welded. The evacuated can assembly is then placed in a HIP
furnace that is pressurized (typically with an inert gas) to a
pressure of at least about 15,000 psi. Simultaneously, induction
coils inside the HIP furnace heat the evacuated can assembly to a
temperature just below the melting point of the parts, typically
about 2200.degree. F. for tool steels. The pressurized evacuated
can assembly is held at this temperature for approximately four
hours, after which the P/M tool steel powder has been solidified
and forged into an inlay having a metallurgical bond (i.e., fused)
with the tool steel valve seat substrate.
Note that the currently practices of various versions of the basic
CIP process described above are all relatively expensive. High
costs are associated with the molds and the tooling for the upper
and lower portions of the can assembly, as well as the special
handling required in welding, pressure testing, evacuating,
crimping, and sealing can assemblies. In fact, the cost of
preparing evacuated can assemblies as described above may
substantially exceed the cost of applying HIP to these same
assemblies.
SUMMARY OF THE INVENTION
Methods and apparatus are disclosed for HIPPING radiused shell
preforms to create substantially nonporous cemented carbide inlays
on metal substrates. A radiused shell preform comprises at least
one metal carbide and at least one nonvolatile cement. The radiused
shell preform may be produced by being machined from bar stock, the
bar stock having been produced earlier from powder comprising at
least one metal carbide and at least one nonvolatile cement.
Alternatively, the radiused shell preform may be produced from
powder comprising at least one metal carbide and at least one
nonvolatile cement which has been compressed (e.g., by CIP) to make
an initial preform, the initial preform then being presintered or
sintered so as to substantially maintain a rigid frusto-conical
shape. Presintering includes being heated sufficiently to cause a
nonvolatile cement (e.g., cobalt, chromium and/or nickel) to adhere
metal carbide particles in a predetermined shape, but not being
heated sufficiently to cause the significant metallic grain growth
that is associated with sintering. The heat of either presintering
or sintering vaporizes any volatile binders (e.g., wax or polymer)
that may be present, meaning that a radiused shell preform may be
incorporated in an assembly for HIPPING (a HIPPING assembly). The
rigid shell of a radiused shell preform has substantially uniform
thickness with a predetermined radius on every edge, each such
radius being a predetermined fraction of the uniform thickness.
Through use of a conforming adjustable sliding element; HIP
pressure is applied to compress the radiused shell preform against
a conforming substrate. The conforming adjustable sliding element
and conforming substrate function together to substantially
preserve the shape of the frusto-conical shell, including its
predetermined edge radii, during HIP. To prevent metal carbides
from contacting surfaces of the conforming adjustable sliding
element and conforming substrate, these conforming surfaces
(including their filleted areas corresponding to edge radii) and/or
the radiused shell preform itself may in certain embodiments be
coated substantially uniformly with at least one nonvolatile
cement. Space around the radiused shell preform is evacuated
without the need to totally enclose the preform and its substrate
in a can (i.e., modified canning). Certain embodiments provide for
leak testing of welded seals prior to application of HIP, and other
embodiments make the use of welded seals unnecessary.
Alternative invention embodiments include methods and apparatus for
making P/M inlays on substrates using improved (modified) versions
of the preforming and/or canning portions of a conventional HIPPED
inlay process. For example, a P/M preform may be formed and
maintained entirely within a circular depression in a substrate
through use of a sliding, sealing element in the form of a circular
ring. The circular ring may have an obverse face that can impart a
desired P/M preform shape by redistributing powder being compressed
by longitudinal movement of the circular ring within the circular
depression. A circular ring may also be used to apply HIP pressure
to a preform, whether the preform is formed within a substrate or
elsewhere.
Apparatus for modified canning to make a valve seat inlay as
described herein may comprise, for example, a forged valve seat
form (i.e., substrate) comprising H13 tool steel and a radiused
shell preform comprising at least one metal carbide and at least
one nonvolatile cement, but no volatile binders (since any that may
have been present earlier were driven off during presintering). The
perform may be a rigid frusto-conical shell symmetrical about a
longitudinal axis and having a substantially uniform thickness and
a predetermined radius on every edge. The frusto-conical shell may
be sloped at an angle between about 20 degrees and about 60 degrees
with respect to the longitudinal axis, and each predetermined
radius may be about 10% to about 50% of the shell's uniform
thickness.
Alternatively, apparatus for modified canning to make a valve seat
inlay may comprise, for example, a forged valve seat form
comprising H13 tool steel, plus commercially available metallic
powder (e.g., the P/M tool steel powders REX 121 or Maxamet) for
the inlays. A suitable P/M metallic powder may comprise, for
example, about 3.4% carbon, about 4.0% chromium, about 10.0%
tungsten, about 5.0% molybdenum, about 9.5% vanadium, about 9.0%
cobalt, and the balance iron. A suitable alternative P/M tool steel
powder may comprise, for example, about 2.15% carbon, about 4.75%
chromium, about 13.0% tungsten, about 6.0% vanadium, about 10.0%
cobalt, and the balance iron. In addition to their availability as
powders, these and other tool steels may also be obtained as solid
bar stock from which radiused shell preforms may be machined. Such
tool steel radiused shell preforms can undergo various heat
treatments, including annealing. In contrast, cemented carbide
radiused shell preforms can not be annealed. And if surface
finishing is desired they must be ground.
Suitable valve seat substrate forms may comprise, for example, a
circular wall around a cylindrical void, the circular wall being
substantially symmetrical about a longitudinal axis and having a
first end spaced apart from a second end, as well as an inner
surface spaced apart from an outer surface. In such valve seat
substrate embodiments, a circular depression in the circular wall
first end extends between the circular wall inner and outer
surfaces. The circular depression comprises cylindrical inner and
outer depression walls that are spaced apart and are coaxial with
the circular wall. The inner and outer depression walls extend from
the circular wall first end toward the circular wall second end to
a depression bottom surface. The depression bottom surface extends
between the inner depression wall and the outer depression wall,
and it may be made to conform to a radiused shell preform.
The above valve seat forms may also comprise a transverse web that
extends from the circular wall inner surface completely across the
cylindrical void adjacent to the circular wall first end. If, for
example, a valve seat substrate is forged, such a transverse web
typically remains when the circular wall is formed, peripheral
portions of the transverse web being integral with the circular
wall inner surface adjacent to the circular wall first end. Such a
transverse web, being formed simultaneously with the circular wall
itself, would normally be removed by a punch process which is part
of the forging operation. In certain embodiments, however, the web
is temporarily retained in the valve seat substrate to assist in
establishing and maintaining a vacuum within the circular
depression until completion of HIP. In this way, the web is made
available for use as little or no additional manufacturing cost.
And if, on the other hand, the web is not temporarily retained in a
valve seat substrate, a removable valve seal plug inserted
slidingly and sealingly within the cylindrical void can assist in
establishing and maintaining a vacuum within the circular
depression until completion of HIP. Still other ways of
establishing and maintaining the desired vacuum within the circular
depression until completion of HIP are described below.
Note that when a circular ring is moved longitudinally within a
circular depression to position a radiused shell preform between a
conforming ring and a conforming depression bottom surface, or to
redistribute metallic powder and compress it against the depression
bottom surface to make a P/M preform, a back pressure may exist
tending to move the ring away from the radiused shell or the
powder. This back pressure may be resisted by, for example,
applying pressure on the ring's reverse face that tends to move the
ring toward the depression bottom. But maintaining such as pressure
on the ring complicates normal handling of certain embodiments of
the invention. In such cases, an alternative way to resist ring
movement due to the back pressure is by creating an interference
fit between the ring and the circular depression. Such an
interference fit may be established between, for example, the
internal diameter of the circular ring and the diameter of the
cylindrical inner wall of the circular depression and/or the outer
diameter of the ring and the diameter of the cylindrical outer wall
of the circular depression. Because P/M preforms that are not
sintered are relatively fragile or deformable when compared with a
presintered or sintered radiused shell preform, the above
interference fits may be used more often with nonsintered P/M
preforms to minimize damage due to handling.
Note also that when a P/M preform shape is being created,
sufficient pressure may be applied to the ring reverse face to
temporarily lock the metallic powder particles together in the
desired shape (i.e., applying sufficient pressure to the metallic
powder to form a "green" powder P/M preform). The latter pressure
is typically substantially higher than the pressure required to
correctly position a ring having an interference fit within a
depression against a radiused shell preform or a previously made
P/M preform.
In the above valve seat assemblies a vacuum of about 0.1 torr or
better must be created in the enclosed space containing the
radiused shell or P/M preform to ensure sufficiently high density
in the valve seat inlay that is formed when the radiused shell or
P/M preform is HIPPED. To make the enclosed space in which the
vacuum will be created, the circular ring may first be moved
longitudinally in the circular depression toward the depression
bottom surface to facilitate compression of a preform. Following
this movement, the ring may be hermetically sealed (as, for
example, by electron beam welding in a vacuum chamber) to the
circular wall first end. Alternatively, a hermetic seal may be
formed over the circular ring and the transverse web by a
deformable circular lid centerable within the peripheral circular
rim. The deformable circular lid is peripherally hermetically
sealable to the peripheral circular rim by, for example, electron
beam welding in a vacuum chamber, and the lid extends over the
circular depression and the transverse web. Note that in certain
embodiments, the deformable circular lid and the circular ring may
be separable, whereas in other embodiments they may form a single
circular lid-ring structure.
When the back pressure phenomenon noted above is counteracted by
creating an interference fit of the circular ring within the
circular depression, there will be a decreased tendency for
handling to degrade a radiused shell or P/M preform within a valve
seat assembly of the invention, even if force on the ring's reverse
face is reduced to zero. Thus, creation of an interference fit
between the circular ring and the circular depression facilitates
handling in certain industrial environments and may be practiced,
although it is not required for all embodiments of the
invention.
Maintenance of a predetermined position of the circular ring within
the circular depression allows production of consistent P/M preform
shapes at lower pressures than those required for making
conventional "green" metallic powder preforms. Even at relatively
low pressures, metallic powder flows in a fluid-like manner to
accommodate the changing shape of the internal space between the
circular ring obverse face and the depression bottom surface.
Meanwhile, the ring's interference fit in the depression prevents
unplanned ring movement that could result in deformation of a P/M
preform or displacement of (and possible damage to) a radiused
shell preform.
As noted above, longitudinal movement of a circular ring toward a
circular depression bottom surface may result from direct pressure
on the ring's reverse face, as by increased ambient pressure or, in
certain embodiments, by pressure exerted by a circular top cap or a
cylindrical ring adjuster that is in contact with the ring's
reverse face. Ring movement may also be achieved through pressure
exerted on a deformable circular lid which, in turn, is in contact
with (and can exert pressure on) the ring's reverse face. Thus, in
certain embodiments, a top cap subassembly may be used (with or
without a cylindrical ring adjuster) to facilitate maintenance of a
vacuum within the depression (i.e., within the enclosed space that
contains a radiused shell or P/M preform). Further description of
the above structures, as well as methods of using them, is provided
below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates a typical valve body and seat
assembly for fracturing pumps, the valve being in the open
position.
FIG. 2 schematically illustrates sand particles and/or aluminum
oxide spheres trapped between mating surfaces during closure of the
valve assembly in FIG. 1.
FIG. 3 schematically illustrates how the slurry particles that are
not expelled from between the valve mating surfaces of FIGS. 1 and
2 are trapped and crushed upon completion of valve closure.
FIG. 4 schematically illustrates a cross-section of a typical
conventional can assembly for HIPPING, wherein the valve seat
substrate and P/M powder inlay preform are totally enclosed by the
upper and lower portions of the can assembly.
FIG. 5 schematically illustrates an exploded cross-sectional view
of one embodiment of a valve seat assembly of the invention,
including a circular ring, a deformable circular lid, and a valve
seat form comprising a circular wall having a peripheral circular
rim, a circular depression, and a transverse web, metallic powder
being located within the circular depression.
FIG. 6A schematically illustrates a cross-sectional view of a
welded valve seat assembly, including a separable circular lid and
circular ring on a valve seat form, after modified canning.
FIG. 6B schematically illustrates a cross-sectional view of the
valve seat assembly shown in FIG. 6A after HIP.
FIG. 7A schematically illustrates a cross-sectional view of a
welded valve seat assembly, including an integral circular lid and
circular ring on a valve seat form, after modified canning.
FIG. 7B schematically illustrates a cross-sectional view of a
welded valve seat assembly, including a circular ring on a valve
seat form, after modified canning.
FIG. 8 schematically illustrates a cross-sectional view of a P/M
inlay on a valve seat form after modified canning, HIP and finish
machining.
FIG. 9A schematically illustrates a cross-sectional view of an
alternative valve seat assembly including a circular ring on a
valve seat form with a valve seat plug under a circular top cap
with magnetic ring restraint on a cylindrical ring adjuster.
FIG. 9B schematically illustrates a cross-sectional view of an
alternative valve seat assembly including a circular lid-ring on a
valve seat form with a transverse web under a circular top with
magnetic lid-ring restraint on a cylindrical ring adjuster.
FIG. 10 schematically illustrates a cross-sectional view of an
alternative valve seat assembly including a circular lid-ring on a
valve seat form with a transverse web under a circular top cap with
magnetic ring restraint.
FIG. 11 schematically illustrates a cross-sectional view of an
alterative valve seat assembly including a circular ring on a valve
seat form and a circular top cap with magnetic ring restraint and a
ring-cap seal.
FIG. 12A schematically illustrates a cross-sectional view of an
alternative valve seat assembly including a circular lid-ring on a
valve seat form with a transverse web and a circular top cap having
an evacuation/pressurization port and magnetic ring restraint in a
shallow counterbore.
FIG. 12B schematically illustrates a cross-sectional view of an
alternative valve seat assembly including a circular ring on a
valve seat form with a transverse web and a circular top cap having
an evacuation/pressurization port with magnetic ring restraint in a
shallow counterbore.
FIG. 13 schematically illustrates a cross-sectional view of an
alternative valve seat assembly including a circular ring on a
valve seat form with a transverse web and a circular top cap having
a dual-passage evacuation/pressurization port without magnetic ring
restraint or a shallow counterbore.
FIG. 14 schematically illustrates a sectional view of a cemented
carbide preform in the shape of a frusto-conical shell.
FIG. 15 schematically illustrates a cross-sectional view showing
the frusto-conical shell of FIG. 14 that has been placed within a
valve seat form into which a sliding element can be inserted.
FIG. 16 schematically illustrates a cross-sectional view of a
machined valve seat form showing a thin sacrificial layer over a
cemented carbide inlay.
FIG. 17 schematically illustrates a cross-sectional view of a
machined valve seat form having a cemented carbide inlay.
DETAILED DESCRIPTION
An exploded cross-sectional view of an example valve seat assembly
99 is schematically illustrated in FIG. 5. A valve seat form 96
comprises circular wall 170 which surrounds cylindrical void 172.
Circular wall 170 is substantially symmetrical about its
longitudinal axis and has a first end 174 spaced apart from a
second end 176, as well as an inner surface 178 spaced apart from
an outer surface 179. In this illustrated embodiment, a circular
depression 180 lies between circular wall inner surface 178 and
circular wall outer surface 179. Circular depression 180 extends
from first end 174 of circular wall 170 toward second end 176 to
depression bottom surface 187. Circular depression 180 comprises
cylindrical inner depression wall 182 and cylindrical outer
depression wall 184. Both inner depression wall 182 and outer
depression wall 184 are coaxial with circular wall 170. Depression
bottom surface 187 extends between inner depression wall 182 and
outer depression wall 184. In valve seat form 96, a transverse web
190 extends from circular wall inner surface 178 completely across
cylindrical void 172 adjacent to circular wall first end 174. In
the illustrated embodiment of FIG. 5 valve seat form 96 has been
forged, and transverse web 190 has been formed simultaneously with
circular wall 170 as described above. Although it will subsequently
be removed, transverse web 190 is temporarily retained in valve
seat form 96 as shown in FIG. 5 to assist in maintaining a vacuum
within circular depression 180 until completion of modified
canning. In certain illustrated embodiments (see, e.g., FIGS. 5,
6A, 6B, and 7A), transverse web 190 comprises a shallow concavity
160 substantially symmetrical about the longitudinal axis and
extending toward second end 176 of circular wall 170.
The illustrated embodiment of circular wall 170 of FIG. 5
additionally comprises a peripheral circular rim 177 on circular
wall first end 174. Circular rim 177 is usable for centering and
peripherally hermetically sealing deformable circular lid 192 to
circular wall first end 174. As illustrated, deformable circular
lid 192 extends over circular depression 180 and transverse web
190. Depression bottom surface 187 comprises at least one circular
sloping surface 186 sloping generally from outer depression wall
184 inward (i.e., toward the longitudinal axis) and simultaneously
toward circular wall second end 176. Depression bottom surface 187
additionally comprises circular flat surface 189 at a substantially
constant depth within circular depression 180. Note that circular
sloping surface 186 is a conical surface symmetrical about the
longitudinal axis in the illustrated embodiment, sloping surface
186 being sloped at an angle of about 60 degrees with respect to
the longitudinal axis. Further, circular depression bottom surface
187 additionally comprises a smoothly curved transition surface 188
between adjacent coaxial circular surfaces 186 and 189 of circular
depression bottom surface 187.
A metallic powder redistribution and compression element in the
form of circular ring 194 is shown in FIG. 5 as being separable
from deformable circular lid 192, but may in other embodiments be
integral with the lid (see, e.g., FIG. 7A). Circular ring 194 is
dimensioned to be closely fitted within and also sealingly movable
longitudinally within circular depression 180. Circular ring 194
comprises an obverse face 198 (for redistributing and compressing
metallic powder), a body 196, and a reverse face 197. Obverse face
198 in turn comprises a powder redistribution feature which, in the
illustrated embodiment, is the conical surface 191. In the
illustrated embodiment of FIG. 6A, the space between conical
surface 191 and depression bottom surface 187 is shown as the space
wherein metallic powder 193 (e.g., P/M tool steel powder as
described above) is redistributed, compressed and retained in a
desired predetermined P/M preform shape.
As noted above, circular ring 194 is dimensioned to be closely
fitted within and also sealingly movable longitudinally within
circular depression 180. Being sealingly movable in circular
depression 180, circular ring 194 prevents the escape of metallic
powder 193 which is redistributed and compressed between a powder
redistribution feature of obverse face 198 and depression bottom
surface 187. This sealing function of circular ring 194 may be
achieved by a close sliding fit of circular ring 194 within
circular depression 180 and/or by an interference fit of circular
ring 194 within circular depression 180.
If such an interference fit is provided, the interference of
circular ring 194 may be with inner depression wall 182 and/or with
outer depression wall 184. If the interference is with either outer
depression wall 184 or inner depression wall 182 (but not both),
then the space within circular depression 180, including that which
is bounded superiorly and inferiorly by obverse face 198 and
depression bottom surface 187 respectively, may be evacuated (e.g.,
in preparation for HIP) even after circular ring 194 has been moved
longitudinally within circular depression 180 to redistribute and
compress metallic powder to form a P/M preform. Evacuation of
circular depression 180, including the space containing the P/M
preform and the interstitial spaces within the P/M preform itself,
is possible through the close sliding clearance between circular
ring 194 and either outer depression wall 184 or inner depression
wall 182. After such evacuation, the space containing the P/M
preform may be hermetically sealed by, for example, placing
deformable lid 192 over circular depression 180 and then welding
the periphery of deformable lid 192 to peripheral rim 177.
Alternatively, circular ring 194 itself may be hermetically sealed
within circular depression 180 by welding circular ring 194 to
inner depression wall 182 and outer depression wall 184. Either of
these options for achieving hermetic sealing of an evacuated space
containing a P/M preform may be carried out in a vacuum chamber
using, for example, electron beam welding. After such hermetic
sealing, the resulting valve seat assembly may be HIPPED.
Note that if an interference fit is provided between circular ring
194 and both inner depression wall 182 and outer depression wall
184 of circular depression 180, then a hermetic sealing of space
within circular depression 180 may be achieved without welding,
simply by moving circular ring 194 longitudinally to insert it
sealingly within circular depression 180. In this case, circular
ring 194 must not be sealingly inserted within circular depression
180 until the space within circular depression 180 has been
evacuated. Such evacuation may be accomplished by placing a valve
seat assembly (comprising a circular wall having a circular
depression containing metallic powder, together with a circular
ring for insertion into the circular depression) within a vacuum
chamber prior to insertion of the circular ring into the circular
depression so as to achieve a hermetic seal and to redistribute and
compress the powder. Alternatively a circular top cap, with
associated components as shown in the illustrative examples herein,
can be used to evacuate circular depression 180 prior to insertion
of circular ring 194. With such use of a circular top cap and
associated components, the space to be evacuated may be confined to
little more than the space within circular depression 180 itself,
rather than the generally much larger space within a vacuum
chamber. Evacuation to an acceptable vacuum (e.g., about 0.1 torr)
will proceed relatively quickly in the former case, with consequent
savings of time and energy. But in either case, the hermetic seal
which exists after circular ring 194 is inserted into circular
depression 180 (and thus the vacuum necessary for successful HIP)
will be maintained around the P/M preform during subsequent HIPPING
of the valve seat assembly.
For valve seat assembly 99' schematically illustrated in FIG. 6A,
an interference fit as described above between circular ring 194
and both inner depression wall 182 and outer depression wall 184 of
circular depression 180 would typically be unnecessary. This is due
to the hermetic seal provided by deformable circular lid 192 being
welded to peripheral circular rim 177 of circular wall 170. Note
that the powder redistribution feature (conical surface 191) of
circular ring 194 has been advanced into contact with metallic
powder 193 within circular depression 180, thus redistributing,
compressing and retaining metallic powder 193 in a predetermined
preform shape between conical surface 191 and depression bottom
surface 187. Note also that deformable circular lid 192 was welded
to peripheral circular rim 177 while the entire valve seat assembly
99' was in a vacuum chamber. Thus, after completion of this welding
as illustrated in FIG. 6A, metallic powder 193 lies distributed,
compressed and retained in a P/M preform shape in an evacuated
space bounded superiorly and inferiorly by conical surface 191 and
depression bottom surface 187 respectively.
Comparing FIGS. 4 and 6A, both drawings schematically represent
valve seat assemblies prior to HIP. And both assemblies produce
analogous final parts (i.e., valve seats substantially as shown in
FIG. 8). But a relatively large number of the assemblies in FIG. 6A
can be compactly stacked like pancakes in a HIP furnace, whereas
fewer of the assemblies in FIG. 4 could be stacked in the same HIP
furnace. Thus the cost of HIPPING one of the assemblies in FIG. 6A
will be significantly less than the cost of HIPPING one of the
assemblies in FIG. 4. Additionally, the post-HIP machining costs
for the assembly in FIG. 6A will be significantly less than the
post-HIP machining cost for the assembly in FIG. 4.
Note in FIG. 6A that a shallow concavity exits in deformable
circular lid 192 that generally matches shallow concavity 160 in
transverse web 190. This lid concavity exists because deformable
circular lid 192 was welded to peripheral circular trim 177 in a
vacuum chamber. When welded assembly 99' is removed from the vacuum
chamber in which circular lid 192 was welded to peripheral circular
rim 177, ambient pressure surrounding welded assembly 99'
(generally, atmospheric pressure) is higher than the near-zero
pressure within the space between deformable circular lid 192 and
transverse web 190. This pressure differential elastically deforms
circular deformable lid 192 as shown. The deformation, in turn,
serves as an inexpensive and reliable tattletale indicator during
quality control inspection to insure that the weld that seals
circular deformable lid 192 to peripheral circular rim 177 is
air-tight (i.e., hermetic). If the tattletale concavity of circular
deformable lid 192 is not present, or if it disappears over time,
the weld seal is shown to be not air-tight, meaning assembly 99'
must be disassembled, evacuated again, and re-welded.
As explained above, the space within circular depression 180 and
between deformable circular lid 192 and transverse web 190 (that
is, space within circular depression 180 and contiguous space),
must be substantially evacuated (i.e., to about 0.1 torr) before
completion of the weld that hermetically seals deformable circular
lid 192 to peripheral circular rim 177. If the evacuation is not
substantially complete within these spaces prior to HIP, the fused
P/M powder will contain porosities. Any such porosity may
constitute a stress riser under cyclic fatigue impact loading,
leading to crack initiation and subsequent failure of the valve
seat. Note in FIG. 6A (i.e., under the influence of ambient
atmospheric pressure) there is still a small gap between deformable
circular lid 192 and transverse web 190 of welded assembly 99'. But
as schematically illustrated in FIG. 6B, welded assembly 99' has
been structurally altered by application of the substantially
higher-than-atmospheric pressure of HIP, the altered welded
assembly being labeled 99''. The gap seen in welded assembly 99' is
not present in altered welded assembly 99'' because deformable
circular lid 192 and transverse web 190 have been fused together
due to the high pressure of the HIP process.
Alternative valve seat assemblies of the invention may comprise
components differing from those illustrated in FIG. 5. For example
deformable circular lid 192 may not be separable from circular ring
194, instead forming a circular lid-ring 194'. Such a valve seat
assembly 98 is schematically illustrated in FIG. 7A. Still another
alternative valve seat assembly 97 is schematically illustrated in
FIG. 7B. Valve seat assembly 97 (FIG. 7B) does not have a
deformable circular lid 192, and it comprises circular wall 170'
which may be compared with circular wall 170 (FIG. 5) except for
the absence of peripheral circular rim 177 and transverse web 190.
As an alternative way of accomplishing the hermetic sealing
function of circular lid 192 when it is welded to peripheral
circular rim 177 (see, for example, FIG. 6A), circular ring 194 of
valve seat assembly 97 is itself hermetically sealable (as, for
example, by electron beam welding) under ambient vacuum to circular
wall 170'. This direct hermetic sealing by welding of circular ring
194 to circular wall 170' obviates the need for circular lid 192,
welded to circular rim 177 as in FIG. 6A, to act in concert with
transverse web 190 to allow metallic powder 193 to be maintained in
a vacuum.
Thus, metallic powder located between circular ring 194 and
depression bottom surface 187, as shown in FIG. 7B, can be
redistributed, compressed and retained under vacuum in a desired
predetermined P/M preform shape via longitudinal adjustment of
circular ring 194 within circular depression 180, followed by
welding of circular ring 194 to circular wall 170' to form hermetic
seals as illustrated in FIG. 7B. Note that if the fit of circular
ring 194 within circular depression 180 is not an interference fit,
continuous force may have to be applied to circular ring 194 both
prior to and during welding of the illustrated seals to ensure that
circular ring 194 does not spring back within circular depression
180 under the influence of back pressure exerted by compressed
metallic powder. The need for such continuous force may be
eliminated by compressing metallic powder within circular
depression 180 by sufficient force on circular ring 194 to form the
powder into a "green" power preform which would exert little or no
back pressure. Alternative ways to eliminate the need for such
continuous force would be to create an interference fit between
circular ring 194 and circular depression 180 as described above.
The amount of interference in such an interference fit may be
chosen to be sufficient to create resistance to longitudinal
movement of circular ring 194 that will counteract the influence of
back pressure exerted during compression of the metallic powder
into a P/M preform.
After welding, the evacuated valve seat assembly 97 containing a
P/M preform may then be subjected to HIP as described above. Note
that during application of HIP to the welded evacuated valve seat
assembly 97, the weld areas sealing circular ring 194 to circular
wall 170' will deform as circular ring 194 is advanced further into
circular depression 180 to increase the density of metallic powder
193 by greater compression against depression bottom surface
187.
Each of the valve seat assemblies disclosed above employs modified
canning to provide an assembly ready for application of HIP which
does not involve total enclosure of the assembly in a can. After
application of HIP to any such assembly employing modified canning,
the assembly is then annealed, finish machined, heat treated,
hardened and tempered to make a tempered valve seat inlay 42. FIG.
8 schematically illustrates a valve seat 95 comprising a tempered
valve seat inlay 42 on a valve seat substrate 41.
The invention includes variations of the methods and apparatus
described herein for obtaining tempered powdered metal inlays on
substrates, the object shown in FIG. 8 being merely an illustrative
example. Two such variations in the apparatus described above are
schematically illustrated in the valve seat assemblies 94 and 93 of
FIGS. 9A and 9B respectively. Note that the valve seat assemblies
shown in FIGS. 5, 6A, 6B, 7A and 7B achieve the hermetic sealing of
evacuated spaces containing P/M preforms, as in certain
embodiments, by welding a circular deformable lid, circular ring or
circular lid-ring to a valve seat form in a vacuum chamber. Because
in each such case the entire assembly is within the vacuum chamber,
the evacuation of space containing the metallic powder intended to
form a valve seat inlay is substantially complete. Such an
evacuation, in turn, substantially eliminates porosity in the fused
P/M powder inlay obtained after HIP is applied.
In contrast, the purpose of assembly 94 in FIG. 9A and assembly 93
in FIG. 9B is in each case to eliminate the need for welding seals
in a vacuum chamber. The hermetic sealing function of welded seals
is replaced in each of these embodiments by an interference fit of
a circular ring within a circular depression. In the embodiment of
FIG. 9A, evacuation of the space within circular depression 180 is
carried out via one or more evacuation/pressurization ports 210 in
a removable (and reusable) circular top cap 204, in conjunction
with a removable (and reusable) valve seat plug 208, and a
removable (and reusable) cylindrical ring adjuster 202. In the
embodiment of FIG. 9B, evacuation of the space within circular
depression 180 is carried out via one or more
evacuation/pressurization ports 210 in a removable (and reusable)
circular top cap 204, in conjunction with a removable (and
reusable) cylindrical ring adjuster 202 and a transverse web 190'.
Note that circular wall 170'' (FIG. 9A) and circular wall 170'''
(FIG. 9B) comprise radiused and/or chamfered upper portions of
inner depression wall 182 and outer depression wall 184 to
facilitate entry of circular ring 194'' (see FIG. 9A) or circular
lid-ring 194''' (see FIG. 9B) into circular depression 180
notwithstanding their interference fit.
Referring to FIG. 9A, the hermetic sealing function of the welded
seals of the valve seat assemblies shown in FIGS. 5, 6A, 6B, 7A and
7B is ultimately replaced by an interference fit between the inner
diameter and the outer diameter of circular ring 194'' with,
respectively, inner depression wall 182 and outer depression wall
184 of circular depression 180 in circular wall 170''. However,
before circular ring 194'' is advanced into circular depression 180
to achieve a hermetic seal, a vacuum must still be established
around the powder within circular depression 180 to eliminate
porosity in the final HIPPED inlay. This vacuum within circular
depression 180 and contiguous space is achieved by withdrawing air
through evacuation/pressurization port 210 from the interior space
bounded by portions of circular top cap 204, cylindrical ring
adjuster 202, valve seat plug 208 and circular wall 170''. After
the desired vacuum is achieved (i.e., about 0.1 torr), circular
ring 194'' may be advanced into circular depression 180 to
redistribute and compress metallic powder within circular
depression 180 as described above to form a P/M powder preform.
Because of the hermetic seal then existing due to the interference
fit of circular ring 194'' with both the inner and outer walls of
circular depression 180, circular top cap 204, cylindrical ring
adjuster 202, and valve seat plug 208 may be removed prior to
application of HIP. This removal may be facilitated by pressurizing
(e.g., by compressed air admitted through evacuation/pressurization
port 210) the interior space bounded by portions of circular top
cap 204, cylindrical ring adjuster 202, valve seat plug 208,
circular ring 194'' and circular wall 170''.
Note that valve seat plug 208 in FIG. 9A is removably inserted
slidingly and sealingly within circular wall 170'' from circular
wall second end 176. Valve seat plug 208 comprises a flange 220 for
contacting circular wall second end 176 to limit insertion of valve
seat plug 208 into circular wall 170''. Valve seat plug 208 also
comprises at least one circumferential seal 216 for sealing valve
seat plug 208 against circular wall inner surface 178 during
sliding insertion of valve seat plug 208 within circular wall
170''. In FIG. 9B, the sealing function of valve seat plug 208 is
not required because valve seat form 96''' comprises transverse web
190'.
In FIG. 9A, circular top cap 204 fits slidingly and sealingly over
circular wall first end 174''. Analogously in FIG. 9B, circular top
cap 204 fits slidingly and sealingly over circular wall first end
174'''. In both FIGS. 9A and 9B, cylindrical ring adjuster 202 fits
slidingly and sealingly within circular top cap 204. As seen in
FIG. 9A, for example, the sliding seal of cylindrical ring adjuster
202 within circular top cap 204 allows cylindrical ring adjuster
202 to move longitudinally to contact circular ring revere face
197'' for moving circular ring 194'' longitudinally within circular
depression 180 toward depression bottom surface 187 for
redistributing and compressing metallic powder within circular
depression 180. But before circular ring 194'' is moved
sufficiently into circular depression 180 to hermetically seal the
metallic-powder-containing portion of circular depression 180,
substantially complete evacuation of this
metallic-powder-containing portion and contiguous space must be
accomplished.
To facilitate this evacuation in the embodiment of FIG. 9A, for
example, circular top cap 204 comprises at least one
evacuation/pressurization port 210 usable for evacuating circular
depression 180 and contiguous space (i.e., space enclosed by
portions of circular wall 170'', circular top cap 204, cylindrical
ring adjuster 202, and valve seat plug 208). Circular top cap 204
also comprises at least one internal circumferential seal 215 for
sealing circular top cap 204 against circular wall outer surface
179'' as circular top cap 204 is fitted slidingly over circular
wall first end 174''. Circular top cap 204 further comprises at
least one internal circumferential seal 218 for sealing circular
top cap 204 against cylindrical ring adjuster 202 as cylindrical
ring adjuster 202 is fitted slidingly within circular top cap 204.
Circumferential seals 215, 218 and 216, functioning with circular
top cap 204, cylindrical ring adjuster 202, and valve seat plug 208
as described herein and shown in FIG. 9A, permit withdrawal of gas
from circular depression 180 and contiguous space.
Analogously, before redistribution and compression of metallic
powder in circular depression 180 in the embodiment of FIG. 9B,
circular depression 180 and contiguous space must be evacuated.
This evacuation is facilitated, as shown in FIG. 9B, by at least
one evacuation/pressurization port 210 in circular top cap 204,
port 210 being usable for evacuating circular depression 180 and
contiguous space (i.e., interior space enclosed by portions of
circular wall 170''', circular top cap 204, cylindrical ring
adjuster 202, and transverse web 190'). circular top cap 204 also
comprises at least one internal circumferential seal 215 for
sealing circular top cap 204 against circular wall outer surface
179''' as circular top cap 204 is fitted slidingly over circular
wall first end 174'''. Circular top cap 204 further comprises at
least one internal circumferential seal 218 for sealing circular
top cap 204 against cylindrical ring adjuster 202 as cylindrical
ring adjuster 202 is fitted slidingly within circular top cap 204.
Circumferential seals 215 and 218, functioning with circular top
cap 204, cylindrical ring adjuster 202, and transverse web 190' as
described herein and shown in FIG. 9B, permit evacuation of
circular depression 180 and contiguous space.
Structural relationships of the valve seat assembly embodiment of
FIG. 9A include circular top cap 204 having first and second
coaxial cylindrical inner surfaces 212 and 214 respectively spaced
apart longitudinally, first cylindrical inner surface 212 (in
conjunction with circumferential seal 218) fitting slidingly and
sealingly over cylindrical ring adjuster 202, and second
cylindrical inner surface 214 (in conjunction with circumferential
seal 215) fitting slidingly and sealingly over circular wall outer
surface 179'' of valve seat form 96''. Evacuation/pressurization
port 210 extends radially through circular top cap 204 between
first and second coaxial cylindrical inner surfaces 212 and 214
respectively.
The embodiment of FIG. 9A schematically illustrates an application
of the invention showing that once circular depression 180 and
contiguous space of valve seat assembly 94 have been evacuated and
circular ring 194'' has been advanced into circular depression 180
sufficiently to form a hermetic seal, circular ring 194'' may then
be advanced further to redistribute and compress metallic powder
within circular depression 180 (i.e., to form a P/M preform).
Following this, circular top cap 204, cylindrical ring adjuster
202, and valve seat plug 208 may be removed as described above. The
remainder of assembly 94 may then, due to its relatively small
size, be packed efficiently in a HIP furnace. HIP pressure
(typically at least about 15,000 psi) forces circular ring 194''
still further into circular depression 180, compressing the P/M
powder preform while maintaining the necessary hermetic seal due to
the interference fit of circular ring 194'' with both inner
depression wall 182 and outer depression wall 184 of circular
depression 180.
Note that during application of HIP, both pressure and temperature
are substantially increased. In particular, HIP pressure rises
sufficiently to force circular ring 194'' to move further into
circular depression 180 notwithstanding resistance to the movement
offered by metallic powder within the depression and by the
interference fit of the ring within the depression. As a result of
this movement, the metallic powder is compressed to a substantially
nonporous state and held in that state by HIP pressure as heat is
applied. When the temperature of circular ring 194'' reaches the
transformation temperature for the steel in the ring, stress
associated with the interference fit of the ring within circular
depression 180 is relieved and the steel of circular ring 194'' is
subject to plastic deformation under the continuing HIP pressure.
Note that circular ring 194'' typically comprises mold steel having
a transformation temperature significantly lower than the
transformation temperature of valve seat form 96''. Thus, even as
circular ring 194'' deforms, there is no plastic deformation of any
portion of circular depression 180 until compression of the
metallic powder to a substantially nonporous state is complete.
This is because valve seat form 96'' (which includes circular
depression 180) comprises a tool steel (such as H13) having a
significantly higher transformation temperature than the steel of
circular ring 194''. This higher temperature is not reached in the
HIP process until after compression of the metallic powder to a
substantially nonporous state has been achieved. Thus the
plastically deforming steel of circular ring 194'' behaves as a
viscous fluid seal that transmits HIP pressure hydraulically (i.e.,
substantially equally) to portions of the inner and outer walls of
circular depression 180 that it contacts, as well as to the
metallic powder within circular depression 180. Since the metallic
powder remains under substantially complete vacuum as it is
compressed and heated to form an inlay through the above process,
finished metal inlays made using the embodiment of FIG. 9A as above
have the desired (i.e., substantially nonporous) character needed
for exceptional durability in service.
Analogously, substantially nonporous metal inlays made using the
embodiment of valve seat assembly 93 in FIG. 9B are also
exceptionally durable. Valve seat assembly 93 comprises a valve
seat form 96'41 which resembles valve seat form 96 in FIG. 5 except
for the absence of circular rim 177 and the presence of radiused
and/or chamfered upper portions of inner depression wall 182 and
outer depression wall 184 of circular depression 180. Because of
the presence of transverse web 190' in valve seat assembly 93,
circumferential seals 215 and 218 can function with circular top
cap 204 and cylindrical ring adjuster 202 as described and shown
above to facilitate evacuation of circular depression 180 and
contiguous space. There is no separate deformable circular lid in
FIG. 9B, but circular lid-ring 194''' is present as an integral
structure. The hermetic sealing function described above for
deformable circular lid 192 in valve seat assembly 99 is performed
in valve seat assembly 93 by an interference fit between the outer
diameter of circular lid-ring 194''' and outer depression wall 184
of circular depression 180 in circular wall 170'''.
In the embodiment schematically illustrated in FIG. 9B, a vacuum
(e.g., about 0.1 torr) must be established around metallic powder
within circular depression 180 before circular lid-ring 194''' is
advanced by cylindrical ring adjuster 202 into circular depression
180 to achieve a hermetic seal. This vacuum is achieved by
withdrawal of air through evacuation/pressurization port 210 from
circular depression 180 and contiguous space. Thus, interior space
bounded by portions of top cap subassembly 201 (which comprises
circular top cap 204 and cylindrical ring adjuster 202), plus
portions of transverse web 190' and valve seat form 96''' is
evacuated. After the desired level of vacuum is achieved (e.g.,
about 0,1 torr), circular lid-ring 194''' may be advanced into
circular depression 180 to redistribute and compress metallic
powder within circular depression 180 as described above to form a
P/M preform. Because of the hermetic seal then existing due to the
interference fit of circular lid-ring 194''' with outer depression
wall 184 of circular depression 180, circular top cap 204 and
cylindrical ring adjuster 202 may be removed prior to application
of HIP. This removal may be facilitated by pressurizing (e.g., by
compressed air admitted through evacuation/pressurization port 210)
the space bounded by portions of circular top cap 204, cylindrical
ring adjuster 202, circular lid-ring 194''', and valve seat form
96'''.
As in FIG. 9A, circular top cap 204 of valve seat assembly 93 in
FIG. 9B has first and second coaxial cylindrical inner surfaces
(respectively 212 and 214), with their respective circumferential
seals 218 and 215 spaced apart longitudinally. First cylindrical
inner surface 212 fits slidingly and sealingly over cylindrical
ring adjuster 202, and second cylindrical inner surface 214 fits
slidingly and sealingly over circular wall outer surface 179''' of
circular wall 170'''. Cylindrical ring adjuster 202 functions with
at least one peripheral sealing element 218 of top cap 204 to
prevent gas passage through the center portion of circular top cap
204. Evacuation/pressurization port 210 extends radially through
circular top cap 204 between top cap first and second coaxial
cylindrical inner surfaces 212 and 214.
Still another embodiment is schematically illustrated as valve seat
assembly 92 in FIG. 10. The hermetic sealing function which permits
evacuation of circular depression 180 and contiguous space in valve
seat assembly 92 is achieved by an interference fit between both
the inner diameter and the outer diameter of circular ring 194''
with inner depression wall 182 and outer depression wall 184
respectively. However, before circular ring 194'' is advanced far
enough into circular depression 180 to achieve a hermetic seal, a
vacuum must be established around the powder within circular
depression 180. This vacuum is achieved by evacuating, through
evacuation/pressurization port 210, the space bounded by portions
of circular top cap 204', valve seat plug 208 and valve seat form
96''. After the desired level of vacuum is achieved (i.e., less
than 0.1 torr), circular ring 194'' may be advanced into circular
depression 180 by pressure exerted on reverse face 197'' of
circular ring 194'' by circular top cap 204'. This advancement of
ciruclar ring 194'' redistributes and compresses metallic powder
within circular depression 180 as described above to form a P/M
preform. Because of the hermetic seal than existing due to the
interference fit of circular ring 194'' with both inner depression
wall 182 and outer depression wall 184 of circular depression 180,
circular top cap 204' and valve seat plug 208 may be removed after
such ring adjustment and prior to application of HIP. Removal of
circular top cap 204' and valve seat plug 208 may be facilitated by
pressurizing (e.g., by compressed air admitted through
evacuation/pressurization port 210) the space bonded by portions of
circular top cap 204', valve seat plug 208, circular ring 194'' and
valve seat form 96''. Note that circular top cap 204' in FIG. 10
extends across the entire first end 174'' of circular wall 170''
and contains at least one peripheral seal 217 to facilitate sliding
and sealing movement over outer surface 179'' of circular wall
170''.
Another embodiment is schematically illustrated as valve seat
assembly 91 in FIG. 11, In this embodiment the hermetic sealing
function which permits evacuation of circular depression 180 and
contiguous space is achieved by an interference fit between both
the inner diameter and the outer diameter of circular ring 194''
with inner depression wall 182 and outer depression wall 184
respectively. But circular ring 194'' is only advanced into
circular depression 180 to achieve such a hermetic seal after a
vacuum is established around the powder within circular depression
180 and contiguous space. This vacuum is achieved by evacuating,
through evacuation/pressurization port 210, the space bounded by
portions of circular top cap 204'', circular ring 194'' (which is
sealed in its contact with top cap 204'' by seal 219) and valve
seat form 96''. Note that the sealing function of the interference
fit between the inner diameter of circular ring 194'' and inner
depression wall 182 after partial advancement of circular ring
194'' into circular depression 180 allows evacuation of circular
depression 180 and contiguous space before contact is made between
the outer diameter of circular ring 194'' and outer depression wall
184. After the desired level of vacuum within circular depression
180 and contiguous space is achieved (i.e., less than 0.1 torr),
circular ring 194'' may be further advanced into circular
depression 180 (by pressure exerted on reverse face 197'' of
circular ring 194'' by circular top cap 204'') to redistribute and
compress metallic powder within circular depression 180 as
described above to form a P/M preform. Because of the hermetic seal
then existing due to the interference fit of circular ring 194''
within circular depression 180, circular top cap 204'' may be
removed prior to application of HIP. This removal may be facilited
by pressurizing (e.g., by compressed air admitted via
evacuation/pressurization port 210) the space bounded by portions
of circular top cap 204'', circular ring 194'' and valve seat form
96''.
Note that circular top cap 204'' in FIG. 11 extends across the
entire first end of valve seat form 96'', as does circular top cap
204' in FIG. 10. Circular top cap 204' comprises a shallow
counterbore 222, and circular top cap 204'' comprises a shallow
counterbore 222'. Both counterbore 222 and counterbore 222' are
centered within their respective circular top caps and are
dimensioned to fit slidingly and sealingly over circular ring
194''. Counterbore 222' has at least one inner circumferential seal
219 for sealing against circular ring 194'' as circular ring 194''
is fitted slidingly within counterbore 222'. Circumferential seal
219 functions with the interference fit between the inner diameter
of circular ring 194'' and inner depression wall 182 (when the
outer diameter of circular ring 194'' has not yet contacted outer
depression wall 184) to facilitate evacuation of circular
depression 180 and contiguous space without the need for valve seat
plug 208 as shown in FIG. 10. Circular top cap 204' and circular
top cap 204'' each, of course, have at least one circumferential
seal 217 for sealing the respective circular top cap against
circular wall outer surface 179'' as the circular top cap is fitted
slidingly over circular wall first end 174'' of valve seat form
96''.
The embodiment schematically illustrated as valve seat assembly 90
in FIG. 12A and valve seat assembly 89 in FIG. 12B each comprise a
valve seat form 96''' having a transverse web 190'. Both circular
top cap 204''' (in FIG. 12A) and circular to cap 204'''' (in FIG.
12B) extend entirely across valve seat form 96'''. In the use of
valve seat assemblies 90 and 89, insertion and removal of a valve
seat plug, as with valve seat assembly 92 (see FIG. 10), is made
unnecessary by the presence of transverse web 190' (which is
removed, for example, during finish machining after formation of a
HIPPED valve seat inlay).
Note that circular lid-ring 194''' in valve seat assembly 90 and
circular ring 194'' in valve seat assembly 80 both function to
provide hermetic sealing of circular depression 180. But circular
lid-ring 194''' is hermetically sealed within circular depression
180 by an interference fit of only its outer diameter with outer
depression wall 184. While in contrast, circular ring 194'' is
hermetically sealed within circular depression 180 by an
interference fit of both its inner and outer diameters with inner
depression wall 182 and outer depression wall 184 respectively.
The circular top caps 204''' and 204'''' in valve seat assemblies
90 and 89 respectively (see FIGS. 12A and 12B) are used generally
as described above for circular top cap 204' in valve seat assembly
92 (see FIG. 10) to establish the required vacuum within circular
depression 180 and contiguous space prior to hermetic sealing as
described above. Following establishment of the required vacuum in
the embodiment of valve seat assembly 90, circular lid-ring 194'''
is moved by pressure applied via circular top cap 204''' into
circular depression 180 to redistribute metallic powder previously
placed there to form a P/M preform, simultaneously creating a
hermetic seal which maintains the P/M preform in a high vacuum.
Analogously, in the embodiment of valve seat assembly 89
establishment of the required vacuum in circular depression 180 and
contiguous space is followed by movement of circular lid-ring 194''
into circular depression 180 by pressure applied via circular top
cap 204''''. After these operations, circular top caps 204''' and
204'''' are removed from their respective valve seat assemblies
using, for example, compressed air as described above. Following
removal of circular top caps 204''' and 204'''', the assemblies
containing the respective P/M preforms may be HIPPED.
Note the use of magnets in FIGS. 9A, 9B, 10, 11, 12A and 12B as
ring retention means for temporarily retaining a circular ring or
circular lid-ring within a circular top cap as the top cap is
fitted slidingly and sealingly over a circular wall first end. Note
also the use of shallow counterbores in FIGS. 9A, 9B, 10, 11, 12A
and 12B as ring centering means for centering a circular ring
retained by ring retention means in a circular top cap. Being so
centered, a circular ring or circular lid-ring will be positioned
for advancement into circular depression 180 as described
above.
An embodiment which does not involve the centering function of a
shallow counterbore as noted above is schematically illustrated in
FIG. 13. A cross-sectional view in FIG. 13 shows an alternative
valve seat assembly 88 having a circular top cap 224 that may be
compared with circular top cap 204'''' in valve seat assembly 89 in
FIG. 12B. Valve seat assembly 89 includes a circular top cap
204'''' having an evacuation/pressurization port 210 with
single-passage access to space enclosed by portions of top cap
204'''', plus magnetic ring restraint and a shallow counterbore 222
for centering the circular ring. But circular top cap 224 has an
evacuation/pressurization port 210' with dual-passage access to
space enclosed by portions of circular top cap 224, without
magnetic ring restraint or a shallow counterbore. This dual-passage
access to space within circular top cap 224 allows relatively
faster evacuation of circular depression 180 and contiguous space
in the embodiment of FIG. 13 than is possible with a single-passage
access such as that schematically shown in assembly 89 (see FIG.
12B).
Note that prior to evacuation of circular depression 180 and
contiguous space in the embodiment of FIG. 13, circular ring 194''
would be advanced far enough into circular depression 180 to center
circular ring 194'' through contact of its inner diameter with
inner depression wall 182. But circular ring 194'' would not be
advanced far enough into circular depression 180 to achieve a
hermetic seal through an interference fit with both inner
depression wall 182 and outer depression wall 184. Without this
hermetic seal, evacuation of the space in which metallic powder
rests within circular depression 180 (and contiguous space) is
possible. Following such evacuation, circular ring 194'' is
advanced far enough into circular depression 180 to redistribute
and compress the metallic powder to make a P/M preform while
simultaneously completing the hermetic seal. This hermetic seal
then maintains the P/M preform under vacuum while top cap 224 is
removed and during the subsequent application of HIP.
The embodiment of FIG. 15 differs from that of FIG. 12B in part
because a radiused shell preform having substantially uniform
thickness and including the predetermined radii 320, 321, 322 and
323 on each edge, such as preform 310 (see FIG. 14), is used in
FIG. 15 instead of P/M powder. The example radiused shell preform
310 comprises at least one metal carbide (e.g., tungsten carbide
and/or vanadium carbide) and at least one nonvolatile cement (e.g.,
cobalt) in a rigid shell shape symmetrical about a longitudinal
axis. The rigid radiused shell preform 310 may be formed in a
separate process (e.g., by machining a preform from bar stock, or
by applying CIP to a powder to make a preform which is then
presintered or sintered) and placed in circular depression 180' for
application of HIP via conforming circular ring 194'''' and
conforming bottom surface 187' (see FIG. 15).
Note that conforming bottom surface 187' functions in conjunction
with conforming circular ring 194'''' to preserve the
frusto-conical shape of radiused shell preform 310, including the
predetermined radii 320, 321, 322 and 323 on each edge, during
application of HIP. By predetermining each shell edge radius as a
function (e.g., about 10% to about 50%) of substantially uniform
shell thickness, edge cracking of HIPPED inlays such as 331 in
valve seat 395 (see FIG. 16) or 332 in valve seat 396 (see FIG. 17)
can be reduced. Note also that due to the rigid shape of radiused
shell preform 310, the slope of the frusto-conical shell (e.g.,
between about 20 degrees and about 60 degrees with respect to the
longitudinal axis), as well as the predetermined radii, remain
substantially unchanged in HIPPED inlays such as 331 and 332.
Sufficient rigidity of the radiused shell preform 310 throughout
HIPPING is maintained by appropriate choice of metal carbide(s),
particle size range, and binder(s) for cementing the particles
together. These choices may in turn be affected by pressures,
temperatures and other conditions when preform 310 was made. For
example, at least one nonvolatile cement may be used to hold metal
carbide particles together. And at least one such nonvolatile
cement may also be applied (after sintering but before HIPPING) as
a substantially uniform coating to an entire radiused shell preform
(and/or to conforming surfaces contacting the preform during
HIPPING). Such coating(s) tend(s) to present any direct contact
between metal carbide particles and substrate metal during HIPPING,
thus reducing the likelihood of high residual stress concentrations
in finished inlays. Additionally, for example, sufficient pressure
might be applied to mechanically lock tungsten carbide and cobalt
particles together in a desired radiused preform shape (including
the predetermined radii 320, 321, 322 and 323 on each edge), or the
particles might be held temporarily in a desired preform shape by a
relatively volatile binder such as wax or polymer. Any such
relatively volatile binder would be driven off by the heat of
presintering or sintering to preserve the desired radiused preform
shape (including the predetermined radii 320, 321, 322 and 323 on
each edge) during handling and subsequent HIPPING.
In any case, the smooth surface 333, the predetermined radii 320,
321, 322 and 323 on each edge, and the angular slope of the
radiused shell preform 310 with respect to its longitudinal axis
are maintained throughout HIPPING, so inlays 331 and 332 and do not
require resurfacing (e.g., as by grinding) in a HIPPED valve seat
such as 395 (see FIG. 16) or 396 (see FIG. 17). Instead,
surrounding material may be machined off just to the level of
surface 333 as in FIG. 17, or a thin sacrificial layer 335 may be
left covering surface 333 as in FIG. 16. Sacrificial layer 335, if
present, will be quickly worn away in use, leaving the hard, dense,
and substantially uniform inlay 331 to resist further wear of valve
seat 395. The manner in which inlay 331 is incorporated in valve
seat 395, as well as the manner in which inlay 332 is incorporated
in valve seat 396, resists shearing forces tending to displace
either inlay during valve closure under high back pressure, tending
to transfer such forces to the surrounding material of each valve
seat.
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